How the data is checked

How Melbourne Solar Data is built.

A number should be understandable before it is impressive. We publish figures only when the source, geography, time period and calculation can be explained clearly. Uncertainty and breaks in a dataset are shown rather than hidden.

1. We keep a dated record of each source

For every dataset used in a published figure, we retain the publisher, source link, release or effective date where supplied, download date, original file information and notes about whether the data is provisional. This makes it possible to check which source stood behind a figure at the time it was published.

For the Clean Energy Regulator solar series, the installation and capacity files must cover the same period before they are used together. Where the file does not contain a separate human-readable “as at” date, we use the end of the latest month represented in the source columns.

The source catalogue was last reviewed on 22 October 2026. Individual metric pages and reports also show the source date used for their figures.

2. Measurement, estimate and recommendation are different things

3. Solar adoption

The Solar Adoption Explorer uses Clean Energy Regulator postcode files as its primary source. The 2001 to 2010 monthly history is combined with the 2011 to present files only after the older monthly totals reconcile with the historical totals carried in the current files.

The source includes certificate-backed new installations, upgrades and stand-alone systems. An installation count is therefore not automatically a count of unique homes with solar, and Melbourne Solar Guide does not turn it into a household penetration rate without a defensible household denominator.

Monthly installation and rated-capacity values are grouped into installation years. “Average recorded capacity” means recorded rated capacity divided by recorded installation events for the same geography and period. It is a derived average, not a median system size.

The current and previous installation year are marked provisional because Small-scale Technology Certificates can be created for up to 12 months after installation. Comparisons using those years need that caveat.

4. Solar System Age Index and 2026 fleet-age report

The Solar System Age Index and 2026 solar fleet age report describe recorded installation cohorts, not the exact age of equipment currently installed at a property. A recorded installation event may relate to a system that has since been removed, replaced or expanded, and the CER series also includes upgrades.

Age thresholds are conservative lower bounds based on the source date and complete installation years. For example, if the source date falls part-way through 2026, a 10+ cohort includes only 2015 or earlier. Some events from 2016 may already be at least ten years old, but an annual cohort cannot identify their installation month reliably, so the whole 2016 cohort is excluded rather than estimated.

The 2026 report applies the same rule to its 10+, 12+ and 15+ year cohorts. For each postcode, the relevant older-cohort count is divided by all recorded installation events in that postcode to calculate the share. Statewide report totals are sums of the same Victorian 3xxx-postcode records, so postcode and statewide figures use the same source and definitions.

The report publishes two different postcode rankings because they answer different questions. The count ranking shows where the greatest number of older recorded events occurred. The share ranking shows where older events make up the largest proportion of recorded activity, and it is limited to postcodes with at least 1,000 recorded installation events to reduce small-denominator distortion. The threshold is a presentation rule, not a statistical claim that smaller postcodes are unimportant.

The downloadable postcode CSV contains the source date, total recorded events, conservative cohort cut-off years, cohort counts and cohort shares. It is generated from the same verified data response as the report, rather than being maintained as a separate spreadsheet.

Older-system concentration can help explain why questions about inverter compatibility, panel capacity, roof work, battery retrofits or full replacement may be relevant. Age alone is never presented as proof that a system is unsafe, defective or due for replacement.

5. Battery adoption has a historical break

Clean Energy Regulator postcode reporting for solar batteries under the Small-scale Renewable Energy Scheme begins from 1 July 2025. Earlier battery information was voluntarily disclosed and is not an equivalent postcode series. We therefore do not draw a continuous postcode trend line across that boundary as though the reporting method had stayed the same.

Solar Victoria battery data can provide useful program-specific context, but it represents installations supported through the Solar Homes Program rather than every Victorian battery installation. Any chart using that source should say so beside the figure.

6. Postcodes, suburbs and councils do not line up neatly

CER installation records are postcode based. ABS Postal Areas are statistical approximations designed to analyse postcode-like geography; they are not official Australia Post boundaries. Suburbs, Postal Areas and Local Government Areas can overlap in ways that make a simple one-to-one comparison misleading.

Suburb guides therefore show postcode data as local context while making clear that the postcode can cover places beyond the named suburb. Council figures use direct council-level sources where possible. We do not allocate postcode totals to councils unless the method and uncertainty can be explained clearly.

7. Penetration metrics need a defensible denominator

“Installations per household” or “solar penetration” should not be calculated by dividing a current installation total by any convenient dwelling number. Census dwelling measures have their own reference year and geography. If a 2021 Census denominator is used beside later solar data, the denominator date must be explicit and the result described as a ratio to the 2021 dwelling base, not a current household penetration rate.

8. Network and export rules differ by distributor

Victoria has five electricity distribution businesses. Their connection processes and flexible-export offers are not interchangeable. The address lookup uses the Victorian Government distributor map to identify the service territory at a property; postcode-only guidance says when more than one distributor may be possible.

Published export guidance is tied to the issuing distributor and the date checked. A network's general connection framework is not treated as a guarantee of the export outcome for an individual property.

9. Equipment popularity is not a quality ranking

Solar Victoria publishes counts of models installed with a Solar Victoria rebate and/or loan. Those datasets can support “most installed within the Solar Homes dataset” analysis. They cannot justify calling a product “best”, and they are not a complete census of Victorian installations.

Where model names need to be grouped by manufacturer, ambiguous names or manufacturer changes are checked manually rather than guessed.

10. Source inventory

11. What is checked before a figure is published?

Different datasets need different checks. For the current CER solar series, the main checks are:

• installation and capacity files cover the same source period;
• current monthly values and historical totals reconcile with the source totals for each postcode;
• the 2001 to 2010 monthly history reconciles with the historical total carried in the current file;
• multiple postcodes are independently spot-checked against the published source;
• missing, zero and not-applicable values remain distinguishable where the source allows it;
• charts, rankings, postcode lookups and downloads derive from the same underlying observations;
• provisional source years remain visibly identified; and
• the source date and calculation notes are visible with the published result.

12. Corrections policy

If a source publisher revises historical data, Melbourne Solar Guide may update the affected figures after checking the revised source. If we find an error in our own calculation, the figure is corrected and a material correction is noted where it could affect how a reader interprets the result.

A published figure should be traceable to the source and method shown on the page. If it cannot be checked that way, it should not be published.